trograph and 1% to the slit imaging system. It
also removes the need for an on-instrument
wavefront sensor for flexure compensation,
with the telescope’s peripheral wavefront
sensor being used for fast tip/tilt and focus
corrections.
The spectrograph subsystem is a gravity-
stable asymmetric white-pupil échelle spec-
trograph, with two arms and volume-phase
holographic grating cross-dispersers. It com-
prises the following key elements:
• An optical table that maintains spectrograph
stability and provides thermal mass for the
environmental enclosure sub-system.
• A Slit Viewer Assembly unit, discussed
above, that directs 99% of the light from
the slit to the collimator.
• A collimator mirror that collimates the
beam from the Slit Viewer Assembly and
directs it to the échelle grating.
• An échelle grating that disperses the light
into the échelle orders.
• Two transfer mirrors: one convex fold mir-
ror and the white pupil relay mirror. The
transfer mirrors and the collimator mirror
together form the white pupil relay that
reimages the pupil of the dispersed light
at the échelle onto the Volume Phase Holo-
graphic gratings.
• A beam splitter that separates the light into
blue and red channels.
• Blue and red gratings that act as both the
cross-dispersers, to separate the échelle or-
ders, and to introduce an anamorphic fac-
tor for more efficient use of the effective
area of the detector in the cross-dispersion
direction.
• Blue and red multi-element camera lenses.
• Blue and red detectors that collect the full
wavelength ranges of each camera, mount-
ed in separate cryostats.
• Focus controls for each camera.
58
GeminiFocus
The team will work the remainder of the
year to complete the final integration and
testing before shipping to Chile near the
end of the year.
SCORPIO: Moving Toward Its
Build Phase
On June 5-7, the SCORPIO project held its
Critical Design Review (CDR) at the South-
west Research Institute (SwRI) headquarters
in San Antonio, Texas. Team members from
SwRI, FRACTAL (an instrument design firm
in Madrid, Spain), Space Telescope Science
Institute, Johns Hopkins University, George
Washington University, and Gemini Observa-
tory, participated in the review, presenting
material to an eight-member external review
committee. John Troeltzsch from Ball Aero-
space and the National Center for Optical-
infrared Astronomy Management Oversight
Council chaired the very experienced exter-
nal review panel.
The reviewers recognized and congratu-
lated the team for the tremendous amount
of work and effort spent in progressing the
project since the Preliminary Design Review.
In the following weeks, Project Executive
Scot Kleinman took the identified concerns,
issues, and risks from both the external re-
view committee and the internal Gemini
staff reviewers and crafted a comprehensive
CDR Executive Report that contained rec-
ommended actions to close out the Design
Phase of the project and reduce risk going
forward into the Build Phase.
We remain confident that the SCORPIO team
will build a successful instrument for Gemini.
SCORPIO is a complex and challenging in-
strument to create, and the finished product
promises to become a major capability at the
Observatory, aiding scientific discovery in
the coming decades.
January 2020 / 2019 Year in Review